Known sensor systems for motor vehicles frequently comprise ultrasonic sensors, such as for instance PDC/PLA sensors and are often employed in various driver assistance systems, such as in particular PDA, PLA, IPA, RPA or the like.
Traditional ultrasonic sensors have a membrane, which is capable of being put into ultrasonic vibrations for emitting an ultrasonic signal by means of a control unit. Further, the membrane is configured to be stimulated by an ultrasonic signal into vibrations that can be captured by the control unit. The emitted ultrasonic signal in this connection is emitted as pulse signal so that the reflected signal is capable of being captured by the membrane. In this way ultrasonic signals emitted by the ultrasonic sensor and reflected by an object can be detected. For protection against external influences, such as e.g. dirt, water, snow, ice, mechanical stresses, or the like, ultrasonic sensors have a sensor housing, which surrounds the membrane as well as possibly further sensitive components of the ultrasonic sensor.
A motor vehicle in operation is regularly exposed to different environmental factors, such as for instance different temperatures, humidity, dirt, or the like. Hereby the sensor housing can be soiled by deposits, in particular of ice, snow, dust, or the like. During driving on a road covered in snow for instance due to the tail turbulences deposits of snow on a tail bumper of the motor vehicle may occur. Ultrasonic sensors mounted in the tail bumper can be soiled or blocked by these snow deposits. When subsequently driving behind a motor vehicle that is driving in front, the tail turbulences of the motor vehicle driving in front can cause snow deposits on a front bumper of the following motor vehicle and thus soil or block the installed ultrasonic sensors.
Such pollutions or blockages of ultrasonic sensors lead to it that an outwardly propagating sound pressure of the ultrasonic sensor is reduced so that an obstacle detection is only to a limited extent possible or not possible at all any more. Further, such pollutions can cause a deception of the ultrasonic sensor so that the ultrasonic sensor detects a close obstacle for instance due to the pollution even if such an obstacle is not present at all. In the extreme case a permanent presence of an obstacle is detected independently of whether or not the obstacle is in actual fact present or not.
A reliable support of a driver of the motor vehicle by the corresponding driver assistance system is thus not guaranteed any longer. Further, such misinformation may confuse or irritate the driver and considerably increase the risk of an accident.
In order to provide relief in such a state, the ultrasonic sensors need to be cleaned. This can for instance be effected manually by the driver or automatically by means of a cleaning device. For this purpose ultrasonic sensors have been developed, which besides an emitting of pulse signals are configured for emitting heat. Such an ultrasonic sensor is known from the DE 10 2013 011 186 A1. The heat can be generated via a heating device as well as the emitting of permanent signals by the membrane of the ultrasonic sensor. The generated heat causes a melting of the snow or ice sticking to the sensor housing. Disadvantageous are a high energy consumption and a high thermal stress on the ultrasonic sensor. Further, various pollutions, such as for instance dust, cannot be removed by means of such ultrasonic sensors.
It is therefore the object of the present invention to create a sensor system, a motor vehicle, as well as a method for cleaning an ultrasonic sensor of a sensor system for a motor vehicle, which remove previously named disadvantages or at least partly remove them. Accordingly, it is the task of the present invention to provide a sensor system for a motor vehicle, a motor vehicle, as well as a method for cleaning an ultrasonic sensor of a sensor system for a motor vehicle, which allow in a simple and low-cost manner for an improved cleaning of the ultrasonic sensor involving reduced energy expense as well as low stress on the ultrasonic sensor.